This application relates generally to the recharging of batteries in electrically powered implantable medical devices (IMDs), such as Active Implantable Medical Devices (AIMD). More specifically, this application relates to efficiently recharging batteries in electrically powered implantable medical devices (IMDs) via inductive charging through the skin of a patient while the patient is mobile or otherwise active.
This application relates generally to the recharging of the power supplies of electrically powered implantable medical devices (IMDs), such as AIMDs including examples like pacemakers, neurostimulators, cochlear implants, among others. This includes the use of rechargeable power supplies that are charged through the skin of the patient using inductive charging techniques. Newer medical implants, such as neurostimulators, can consume large amounts of power in comparison to older devices, such as pacemakers, which tend to provide lower power signals. Thus, some current and future medical implants will require more frequent charging than their older counterparts. Some current neurostimulators require that the implant be recharged at intervals of every two weeks or less, and thus patients expend a considerable amount of time charging their IMDs.
Charging times for the rechargeable power supplies for IMDs are limited by a number of factors. In the past, battery chemistries have limited the rate at which an implant could be recharged. However, with the introduction of newer lithium ion batteries and other chemistries, battery chemistry is no longer the primary limitation to recharging of IMDs. During charging, some of the energy that is inductively transferred to the IMD is converted into heat instead of being converted into electricity for charging. Eddy currents form on the housing of the IMD during charging and these currents dissipate as heat. Also, some of the energy used in the recharging circuitry within the IMD is also converted into heat.
Furthermore, the traditional recharging process for IMDs requires that a user sit relatively still during the recharging period to maintain effective alignment between the IMD and an external charging unit which provides the inductive (power) signal that is converted into electricity for charging the IMD batteries. Movement by the user can cause a slight misalignment between the external charger transmitting coil and the internal charger receiving coil, which can cause prevent an effective coupling, reducing the ability to quickly charge the batter if not compensated for. Traditionally, this misalignment was minimized by avoiding user activity during the charging period, but besides often being ineffective, this is inconvenient for the user. It is desirable to allow the user to be more active during the charging process, in order to avoid inconveniencing the users.
Furthermore, because different users will desire to have different movement or activity levels during charging, and thus will likely have different alignment issues arise during the recharging process, it is desirable to have a charging process that is flexible enough to accommodate these differences in a cost effective and flexible manner.